This invention relates to olefin polymerization catalysts and more particularly to supported catalysts comprised of certain titanium-phosphorous-chromium adducts.
The use of chromium compounds in the polymerization of olefins is well-known. U.S. Pat. Nos. 2,825,721 and 2,951,816 teach the use of CrO.sub.3 supported on an inorganic material such as silica, alumina or combinations of silica and alumina, and activated by heating in reducing atmospheres, to polymerize olefins. When, however, a catalyst system of this type is used in techniques such as the well-known particle-form process, the resins produced, while useful in many applications, are unsatisfactory for others because of a deficiency in certain properties such as melt index.
Attempts to improve the properties of polyolefins produced using supported, heat-activated chromium oxide catalysts have been made by adding various compounds to the supported chromium oxide prior to the heat activation thereof. For example, U.S. Pat. No. 3,622,522 shows that an alkoxide of gallium or tin may be added to supported chromium oxide prior to heat activation (and compares addition of aluminum isopropoxide unfavorably). U.S. Pat. No. 3,715,321 suggests adding a compound of a Group II-A or Group III-B metal to supported chromium oxide prior to heat treatment, whereas U.S. Pat. No. 3,780,011 discloses adding alkyl esters of titanium, vanadium or boron, and U.S. Pat. No. 3,484,428 discloses adding alkyl boranes to such a catalyst.
It is also known to utilize other chromium compounds as catalysts for the polymerization of olefins. Such compounds include various silyl chromate and polyalicyclic chromate esters as described, for example, in U.S. Pat. Nos. 3,324,095; 3,324,101; 3,642,749; and 3,704,287. The use of phosphorus-containing chromate esters in olefin polymerization catalysts has also been disclosed in the aforesaid U.S. Pat. No. 3,704,287; and in U.S. Pat. No. 3,474,080.
Use of the above chromium compound catalysts in Ziegler-type coordination catalyst systems has also been proposed. As is well-known in the art, such catalysts frequently additionally comprise organometallic reducing agents such as, for example, trialkyl aluminum compounds. Ziegler-type catalyst systems incorporating supported chromium compound catalysts and organometallic reducing agents, particularly organoaluminum compounds, are disclosed, for example, in U.S. Pat. Nos. 3,324,101; 3,642,749; 3,704,287; 3,806,500.
Numerous other olefin polymerization catalysts and processes are known. For example, U.S. Pat. No. 4,115,318 discloses the polymerization of alpha-olefins at high levels to desirably high melt index employing a supported hydrated or anhydrous polymeric chromium (III) compound such as poly(di-.mu.-dihydrocarbylphosphinatohydroxyaquochromium (III)) activated by heat in a nonreducing atmosphere.
U.S. Pat. No. 3,752,795 discloses the polymerization of olefins in the presence of a catalyst system comprised of an organic-solvent-soluble composition prepared by reaction of an organotitanate with a chromium oxide and an organoaluminum compound to form polymers having controllable molecular weight distributions.
In another U.S. Pat. No. 3,985,676 it is disclosed that olefins polymerized in the presence of reaction products of organophosphorus compounds, such as organophosphites or organophosphates, and chromium trioxide produce polymers particularly well adapted for molding operations.
Still others, for example U.S. Pat. Nos. 3,984,351, and 3,969,272, disclose that polyolefins having improved melt indexes and other advantages are prepared with certain supported catalysts comprised of certain chromium or organophosphoryl chromium reaction products and certain aluminum compounds.
Other processes for the production of polyolefins having improved melt indexes are also known. Such a process employing a catalyst system of chromium and titanium is found in U.S. Pat. No. 3,622,521.
U.S. Pat. No. 4,008,359 and U.S. Pat. No. 3,901,825 disclose still another polymerization process wherein products having improved properties are formed. The catalyst system is one formed by mixing a chromium trisdiorgano-orthophosphate, an alkyl aluminum compound and a halogenated olefin. Other chromium and/or titanium compound catalysts useful in olefin polymerization processes are disclosed in U.S. Pat. Nos. 3,970,613, U.S. 4,041,224, 4,035,560, 3,976,632.